An evaporative cooler is a device that cools air through the evaporation of water. Existing evaporative cooling devices are typically rectangular in shape and have a shallow water reservoir which is supplied by the plumbing of the structure being cooled. A pump pulls water from the reservoir and pumps it through tubing to the top of the unit, where it flows down the sides and through pads that line the sides of the unit. An electric motor powers a fan in the center of the device, which serves to draw outside air through the pads and into the unit.
As the warm, outside air is drawn in through the porous pads by the fan, the latent heat in the air causes water flowing through the pads to evaporate. This evaporation is caused by a transfer of heat from the air to the water. This results in a net loss of heat in the air or, in other words, cooling. The now cooled air is then forced through an exit duct and into the area to be cooled.
Various types of evaporating cooling devices exist, including direct evaporative coolers, indirect evaporative coolers, and two-stage evaporative coolers, also known as indirect-direct evaporative coolers.
Direct evaporative coolers force outside air through a moist evaporative pad to produce cooled air prior to distributing the cool air to a target area. As discussed above, direct evaporative coolers typically have a blower or centrifugal fan that forces the outside air in through the evaporative pad to cool the air, and then out of the device into the target area.
Indirect evaporative coolers are similar to direct evaporative coolers, but instead utilize some type of heat exchanger. For example, in one type of indirect evaporative cooler, processing air is drawn into the device where heat in the air is absorbed by water in an air-to-water heat exchanger to produce cooled air. The heat in the water is then rejected in a cooling tower where the evaporation occurs. In this sense, indirect evaporative closed systems in that the water in the heat exchange absorbs heat from the air, rejects heat to atmosphere in a cooling tower, and recirculates to absorb more heat from the air. Typically, rather than distributing the cooled air into the target area directly, however, the device secondarily performs a heat exchanging process of reducing the temperature of inlet air by the cooled processing air, thus indirectly cooling the inlet air prior to distributing the air to the target room. Accordingly, the cooled, moist processing air never comes in direct contact with the cooled air entering the target area.
Lastly, indirect-direct evaporative coolers use both direct and indirect evaporative cooling in a two-stage process. In the first stage, warm air is pre-cooled indirectly without adding humidity (such as, for example, by passing inside a heat exchange that is cooled by evaporation on the outside). In the direct stage, the pre-cooled air passes through a water-soaked pad and picks up humidity as it cools. Since the air supply is pre-cooled in the first stage, less humidity is transferred in the direct stage, to reach the desired cooling temperatures. This results in cooler air with a relative humidity between 50-70%, depending on the climate, compared to a traditional system that produces about 70-80% relative humidity in the conditioned air.
As will be readily appreciated, water is a critical natural resource. As the available supply of water is becoming outstripped by demand, the cost of potable water may increase to the point where using it for air conditioning purposes, such is in evaporative coolers, could become prohibitive.
Accordingly, there is a need for an evaporative cooling device that requires less water to cool air than is typically required for existing devices.